[palmor]

Please eplain, then, how exactly a picture taken with a 135mm lens on a Pentax DSLR differs from a picture taken with a 200mm lens on a 35mm film camera. That is, given a print made of both images, how would you know which was which? or is it simply that the viewfinder on the film picture provides a larger view of the same scene? that much is, as I already mentioned, certainly true.

The point is that you have more detail on the FF image because the magnification of your lens is higher. You can agree that cropping an image will results in some loss of IQ right? So you're taking an essentially cropped image from the Pentax DSLR vs a non cropped image from a FF DSLR that is using a higher magnification lens.

If magnification of a lens didn't matter why not shoot everything with a 50mm lens and crop the hell out of it. Again a 400mm lens on no matter what size sensor will provide the resolution of that 400mm lens. By saying that there is no difference between the actual focal length of the lens and an equiv FOV you are implying (incorrectly) that the resolution of a 400mm lens on a cropped sensor equals the resolution of a 600mm lens on a FF.

Another example.. I take a photo of a bird with a 400mm lens on my K20d, it takes up 'x' amount of space on my print. I now take the same photo with a 600mm lens on a FF lens. It will take the same 'x' amount of space on the print. Now guess what, I get to crop that FF image by 1.5x and fill my photo with the bird AND I retain MORE detail because I took it with a higher magnification lens. To get the same image now with the Pentax I will have to crop ANOTHER 1.5x, loosing a lot more detail.


John

[palmor]

Yes, although I believe you'd actually need a 22.5MP sensor to have the cropped image come out the same pixel-by-pixel - it needs to be 1.5X the size in both directions.



Right, and as far as I am concerned, that's the end of the story. Most of what after this is a function of having more resolution on the 15MP (actually 22.5MP) camera, not because of any difference between the lenses.



You'll get more detail mostly because you have a higher resolution sensor. Now, if the 300mm lens *happens* to provide more absolute resolution than the 200mm lens, then you might also get a contribution from that effect. But merely being a 300mm lens won't magically give it more resolving power than a 200mm lens.

Now, don't get me wrong - in another thread, I tried arguing a similar thing to what you are saying here: that the 300mm lens on FF/35mm would provide more resolution than the 200mm lens on APS-C, all else equal. Folks did a pretty good job of convincing me that thijust wasn't likely to be much of an issue in practice.

And in any case, now we're arguing about fairly subtle points of resolution and which lens will produce more resolution than which on a sensor of a given pixel count, and ther are just tons of variables at play here. This is a totally different discussion than the general one about the difference between "reach" and FOV. The statements made earlier implied something far more than just subtle difference in resolution that might or might not be visible depending on the relative quality of the lenses or the number of pixels on each sensor.

I think we are going to have to agree to disagree . Give me the choice of a 400mm or 600mm lens for wildlife and I'll take the 600mm lens any day on any size sensor and nobody will ever convince me that the 400mm lens on the 1.5x cropped sensor is the same


John

[Marc Sabatella]

The point is that you have more detail on the FF image because the magnification of your lens is higher.

Not necessarily. The *size* of the image on the sensor isn't that important - what matters is the *resolution* of the lens, and also of the sensor.

If magnification of a lens didn't matter why not shoot everything with a 50mm lens and crop the hell out of it.

Because now you're dealing with a fixed lens resolution and fixed sensor resolution. We wer talking about *different* lenses on *different* cameras, which introduce their own resolution issue. It's entirely possible - indeed, pretty much a certaintly - that a highly-resolving 50mm lens on a high-resolution APS-C sensor *would* fact outperform a poorly-resolving 300mm lens on a low-resolution FF sensor.

Another example.

Since that's the same example I alread responded to previously, I'll let my previous response stand.

[Marc Sabatella]

I think we are going to have to agree to disagree . Give me the choice of a 400mm or 600mm lens for wildlife and I'll take the 600mm lens any day on any size sensor and nobody will ever convince me that the 400mm lens on the 1.5x cropped sensor is the same

Well, I guess if you're saying that facts won't convince you, then you are right - we will have to disagree here. The fact is, a 600mm lens on FF *might* outperform the 400mm lens on APS-C, but it will depend on the relative resolutions of the lenses and sensors involved. The mere fact that one lens has a longer focal length won't magically make it so.

And in any case, again, what you're talking about now is potentially differences in *resolution*, which is not at all what was originally being discussed - the word "reach" implies something far different. If you want to say that the 600mm lens on FF has the same reach as as the 400mm on APS-C but *might* produce more resolution, if all the other numbers line up correctly, that much I could agree on.

[Blue]

Right - because my point is, these are one and the same. It is impossible to alter one without a corresponding change in the other. There is no way to create a lens that provides more "reach" than another on a given camera except by having it create a narrower FOV. And vice versa. Similarly, it is impossible to create a camera has a cropped sensor compared to another - and thus a narrower FOV - without also increasing the "magnification" of any lens attached, assuming you print your pictures at the same size.

Now, it is true the size of the image *on the sensor* won't change with "crop factor". Thus, in this sense, we could possible say that magnification hasn't changed. This will become relevant on the same way someone invents a device that allows us to actually see that image. But in the world as it exists today, the only way to see an image captured by a sensor is to display it on a screen or print it. And assuming one does so at the same size, you get the same magnification aka "reach". There is simply no *real world* sense in which there is an difference whatsoever between FOV and "reach".

Looked at another way - or, rather to restate what I wrote before - if you take a picture on a 35mm film (or "FF" digital) camera with a 450mm lens and I take one of the same scene on an APS-C digital camera with a 300mm lens, and we both make prints of our images, no one on this earth could tell the difference based on "reach" - it will be identical.



Indeed, that is exactly how the crop factor works. It's also *exactly* what happens if you shot with a 750mm lens on the film camera. By the time you make the print, there will be nothing whatsoever about it that would possibly allow anyone to tell whether it came from a 750mm lens on film or a 500mm lens on the K200D. Have you ever worked with film? Have you ever seen an enlarger? Have you ever scanned a negative or positive film? Because most finished product rarely include the complete negative. You are hiding behind the fact that the image on aps-c sensor is cropped.



No doubt there - I do realize that "focal length" has a precise definition and that this does not change. But when FOV changes, so does reach when dealing with the real world of prints and images made visible on screen.



10X? Ten times what? The image will be tiny on the negative itself or on the sensor - clearly not 10 times actual life size. And you can print the image at whatever size you want. It could be printed on a postage stamp and be a small fraction of life size, or be printed on a billboard and be many times larger than life. Maybe you meant ten times larger than a simlarly-presented image made with a 50mm lens? Perhaps - I'm not sure how the math works out there. But there is nothing particularly special about 50mm in this context. And in an event, given that the printed or otherwise-presented image from the 50mm lens will also have more "reach" on than the K20D than on the Super Program, this argument doesn't actually demonstrate anything.



Indeed, but it was really the only sense in which I could see there being any real world difference between 450mm on film and 300mm on APS-C.

The sarcasm isn't really helping in the discussion. You new very well that that 10x was in relation to a 50mm lens which you now is considered normal in that its FOV on 35mm film is roughly equal to the FOV of the human eye. That's basic photography and you knew that. In the case of wildlife photography, the magnification of the lens is very important when the photographer is in the field. That is the whole point of this thread.

Again, why aren't the DA 70 ltd lenses labeled as 105mm or the DA* 300mm listed as DA* 450mm? Because they aren't.

Edit: Magnification clarification: Lens focal length determines its angle of view, and how much the subject will be magnified for a given photographic position. The focal length requirements may be different for a 35mm film camera and a k20d, but a 500mm lens is still a 500mm lens.

[Branimir]

On the funny side...
Have you considered this lens?
I believe it has all the reach one can need (beside Hubble telescope)

B.

[Marc Sabatella]

You new very well that that 10x was in relation to a 50mm lens which you now is considered normal in that its FOV on 35mm film is roughly equal to the FOV of the human eye.

Actually while I suspected that might be what you might have meant, I was baffled as to why you thought that would help prove your case, as it would have seemed rather obvious I would turn around a point out that 50mm on APS-C has more "reach" than 50mm on film, too. So I honestly wasn't sure what you really meant.

In the case of wildlife photography, the magnification of the lens is very important when the photographer is in the field. That is the whole point of this thread.

Indeed, which is is why I am going to such lengths to try to demonstrate that a 450mm lens on APS-C *does* have the same "magnification" in every meaningful real world sense a a 300m lens on 35mm film.

Again, why aren't the DA 70 ltd lenses labeled as 105mm or the DA* 300mm listed as DA* 450mm? Because they aren't.

Absolutely. Focal length doesn't change with sensor size; we all knwo that. FOV changes, and with it, "reach" in every meaningful sense.

lens focal length determines its angle of view, and how much the subject will be magnified for a given photographic position.

"Magnified" compared to what, and why? As I said, sure, I'll agree the image *on the sensor* is the same for the 300mm lens on APS-C and 35mm, and hence in that sense there is no additional magnification *on the sensor*. but since we can't see the image on the sensor, why shoudl that matter? We see *prints*, or images *displayed on screen*. And for a given print size or screen display size, the 300mm lens on APS-C *will* produce 1.5 times more magnification.

[wildman]

So my question are what would a scope give/not
give me that a reg camera lens will give me?

Thanks
Jim

I shoot with a variety scopes for birds and I'll give you my opinion on
it.

First of all field craft and a lot of patience is the single most
important piece of "gear" you can bring to bird photography. Don't think
you are just going to wander off into the woods and be presented with
endless opportunities for great bird shots just because you have
invested a small fortune in hardware. It just doesn't work that way.

You must know something about bird behavior, habitat, along with a lot
of patience. The opportunity for a great bird shot is more often created by
the the photographer and not just the result of dumb luck.

Enough said on this topic for now.

HARDWARE:

Without getting into endless technical discussions I'll just give you my
best opinion, based on my experience, on what I think you should have up
front.

Go out and buy a high quality APO triplet astro scope of about 600mm FL
with a aperture of about 100mm and a good barlow (it's like a TC on a
telephoto) and a heavy duty tripod with a fork mount on it. This would
give you about 18x at f/6 at prime focus and 36x at f/12 barlowed.

To save me a lot of time at this computer if you have more questions in
detail just ask.

Wildman

[Wheatfield]

Your definition of reach is hilarious because you turn around and describe FOV. Reach has to do with magnification. The focal length of a lens is what determines the magnification at which it images distant objects. The FOV changes because of the change in the sensor size. In this case the size of a 35mm negative and aps-c sensor. The crop factor or focal length multiplier is used to get the equivalent FOV.

Some people understand that it is referring to FOV. Because it is stated as equivalent focal length there are many people that don't. In this particular example, I think reach is more important than FOV. If you were to take a picture with a 500mm lens on film and with a K200d, and were to crop the negative during scanning it, you would get a similar print.

The point being, regardless of which camera a 500mm lens is on, it is still a 500mm lens. T he magnification will be 10x on a SuperProgram or K20d. It isn't going to be magnified any more. Sure, you can do a "digital zoom" but that is similar to enlarging a negative in the dark room and the digital image is pre-cropped.

Maybe Falconeye or Wheatfield can do a better job of explaining this.


Also, it would be good to leave binoculars and telescopes out of this because of the eye-piece role in magnification etc.

This is why I hate the whole crop factor thing. If they want to do something that is both precise and non confusing, they should be using the term "magnification factor" or something similar (Pentax DSLR is a ~1.5x magnification factor),
With the APS-C format (another imprecise term), the standard lens is ~32.5 mm if we allow the convention that the standard lens is somewhat longer than the diagonal of the format, as we accepted it for 35mm.
Considering that there is no lens in this precise focal length, lets say for the sake of conversation and easy math that the new DA35mmLTD is as close as we can get to a standard lens with Pentax digital designed glass.
So, this would make a lens in the 350mm range a 10X magnification for this format, and a 500mm lens closer to a 15x magnification.

[Blue]

This is why I hate the whole crop factor thing. If they want to do something that is both precise and non confusing, they should be using the term "magnification factor" or something similar (Pentax DSLR is a ~1.5x magnification factor),
With the APS-C format (another imprecise term), the standard lens is ~32.5 mm if we allow the convention that the standard lens is somewhat longer than the diagonal of the format, as we accepted it for 35mm.
Considering that there is no lens in this precise focal length, lets say for the sake of conversation and easy math that the new DA35mmLTD is as close as we can get to a standard lens with Pentax digital designed glass.
So, this would make a lens in the 350mm range a 10X magnification for this format, and a 500mm lens closer to a 15x magnification.

Some manufacturers kind of do that in some of the P & S cameras by using the term optical and digital magnification.

[Blue]

On the funny side...
Have you considered this lens?
I believe it has all the reach one can need (beside Hubble telescope)

B.

I've seen that before. It would have to be mounted on a tracked vehicle chassis for field use!

[Marc Sabatella]

The sarcasm isn't really helping in the discussion.

BTW, you are right about that; please accept my apology.

[Ron Boggs]

These photos came from an FA*600/4 which is often not long enough for bird work. The key to bird work is blinds... or finding them where they feed...or finding them where they rest. I'm not a fan of shooting at the feeders in my yard, just too easy I guess...but working around feeders is a key technique for great bird photos--see Birds and Blooms magazine for lots and lots of this type of work.

First shot is my opinion of the field of view "discussion"---YAWN--scanned film btw.

Wanted to post some shots from smaller 300mm plus tc but I have a dead external hard drive so only have a few from the card for my digital frame...

[vizjerei]

These are from smc 400mm manual lens. Not cropped.
key: stay one step ahead, walk slowly, stand still, and no sudden movement.

[RioRico]

If I may, I'll add my own take on this. Back in the day, I owned an Olympus PenFT system. That is a half-frame 35mm SLR. The pentaprism was mounted vertically, internally, making it a ZOWIE! tiny SLR, about the same size as the later Oly XA. Each exposed frame was the same size as a 35mm cine frame (half of a 35mm still frame) or very nearly the size of an APS-C sensor. FF= 36x24mm; HF= 18x24mm.

I also had a Canon Dial-35, and other Canon half-frame rangefinders. What a perv! And I owned a Spiratone 400mm tele on a T-mount adapter for the PenFt. With a different T-mount, I could put that 400 on a full-frame Spotmatic or K1000 or whatever.

So let's say I load up the PenFT and the K1000 with Plus-X. I mount the 400 on the Oly HF, focus on a girl sitting on a park bench, fill the frame with her, and shoot. Now, staying in my same shooting position, I put the 400 on the Pentax FF, focus and shoot. Then I reluctantly get up and head for the darkroom.

I develop the film rolls. I put the Pentax FF neg in the enlarger, set to fill an 8x10 sheet (probably cut from a roll I bought mail-order from Freestyle). Print, develop, fix, dry. Now I put the Oly HF neg in the same unmoved enlarger. That HF frame is only going to fill a 5x8 area of paper, so I've cut a smaller sheet. What a cheapskate! Print, dry, compare.

The resolution of those two prints will be exactly the same. The AREA of the HF print will be much less than that of the FF print, which has a wider background - more trees and dogs, etc. Absent subject movement, I would get precisely the same print by cropping the FF print down to the size of the HF.

Looking thru that same lens on those two cams, the FOV of the HF would be less than the FF. Hey, that 400mm has effectively become a 600mm! Que Milagro! No, not really. It's still a 400. The lens-to-film distance is the same. And that's how it works with APS-C vs FF digicams with the same pixel density. A 400 is still a 400; the frame / sensor size determines how much of that 400 image is recorded, the FOV. We haven't changed the focal length, just the area of image that's recorded.

I think I have that right.